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Mr Imran Jawaid - Ophthalmology StR

Mr Richard Stead - Consultant Ophthalmologist, sub-specialising in Glaucoma

Professor Anthony King – Consultant Ophthalmologist, sub-specialising in Glaucoma

An asymptomatic 45 year old Caucasian lady presents for a routine sight test. GAT measurements are right 36mmHg and left 35mmHg. She is hyperopic R +5.00DS VA 6/6 L +5.50DS VA6/6. The visual fields are full and the optic discs appear healthy. How would you manage this patient?

It is not uncommon to find yourself in eye casualty with a referral similar to this. Revised NICE Glaucoma guidelines(1) recommend referral for patients with Intra-Ocular Pressure (IOP) of greater than 24mmHg and it would be ususal for optometrists to send patients with this level of IOP to eye casualty with concerns about the elevated IOP.

However, the key question in such patients is to determine why the pressure is elevated. The answer often lies in assessment of the angle morphology. Worldwide, angle closure may make up one-third of primary glaucoma with the other two-thirds being open angle glaucoma. However the rates of blindness in the two groups are reported as 1:1.(2) The prevalence of angle closure in Europeans has been estimated at 0.4%(3). This is 3-4 times more than previously thought.

Asymptomatic IOP elevation is not unusual. Most patients with primary angle closure glaucoma (PACG) are asymptomatic (unless acute primary angle closure episode)(4,5) In those presenting with elevated IOP the distinction between POAG and PACG is important as the mechanisms underlying their aetiology are very different and consequently the approaches to their management are also different.

Given the previous statements it has been suggested that all primary glaucoma cases should be thought to be primary angle closure glaucoma (PACG) until the angle is proven to be open on gonioscopy(3)

The primary investigation in this patient is gonioscopy. This will reveal either appositional or synechial angle closure, as well as excluding secondary causes of open-angle glaucoma such as pseudoexfoliation and pigment dispersion. This patient is significantly hyperopic which is a risk factor for PAC.

The raised IOP in this case is likely to be a consequence of reduced aqueous outflow through the trabecular meshwork. This may be due to appositional or synechial contact with the iris and/or damage to the trabecular meshwork through contact with the iris, or, meshwork damage from elevated pressure. On gonioscopy one would see Irido-Trabecular-Contact (ITC); simply this is where the iris is in contact with the trabecular meshwork and so the only angle structures visible would be Schwalbe’s line. The European Glaucoma Society has published terminology and guidance for glaucoma. This can be used to define angle closure and guide management(6). The important factor to point out is that the original definition by Foster et al.(7) used a cut-off of 270 degrees of Irido-Trabecular Contact (ITC) but this was found to exclude significant numbers of patients with PAS and optic neuropathy from being correctly described as PACG(8). Currently, agreed consensus is that of 180 degrees of ITC:

Primary angle closure suspect (PACS)

Here there are 2 or more quadrants of ITC. However, IOP, fields and disc are normal.

Primary Angle Closure (PAC)

There are 2 or more quadrants of ITC and elevated pressure and/or peripheral anterior synechiae. Fields and disc are normal.

Primary Angle Closure Glaucoma (PACG)

ITC in 2 or more quadrants with evidence of glaucomatous optic neuropathy.

Acute Primary Angle Closure Glaucoma (APAC)

This is acute angle closure. Patients present with reduced vision, nausea and vomiting is common, markedly elevated IOP, corneal oedema and mid-dilated non-reactive pupil. Often the fellow eye demonstrates feature of PACS or PAC.

Once PAC has been established as the cause it is necessary to explore the exact underlying mechanism; Why is there ITC? The most likely reason is relative pupillary block. This is appositional closure between the posterior iris margin and anterior lens surface; preventing aqueous flow through the pupil. This leads to retention of aqueous in the posterior chamber and anterior bowing of the peripheral iris causing appositional closure of the corneo-scleral angle, thus preventing aqueous outflow and raising IOP. In this situation, a YAG peripheral iridotomy will convert the situation into a single chamber and relieve the pressure differential. This allows the iris to move away from the trabecular meshwork (unless permanent adhesions have formed – Peripheral Anterior Synechiae (PAS)).

Mechanisms which may contribute to the obstruction of aqueous flow can be described using four anatomical levels as described by Ritch and Lowe(9). Here level I pertains to the Iris (e.g. pupil-block, fibrin contraction), level II to the ciliary body (e.g. cysts), level III to the lens (e.g. subluxation, anteriorly positioned lens) and level IV to vectors posterior to the lens (e.g. aqueous misdirection).

The next question is; How should we manage this patient with PAC?

The literature concerning the natural history of angle closure disease is limited. Thomas and colleagues found the 5 year incidence of PAC in patients that had PACS was 22%(10). They went on to show the 5 year incidence of PACG in those with PAC was 28.5% (CI 12%-45%)(11). Both of these studies were limited by small sample sizes. We know that treating fellow eyes (with iridectomy) of those patients with acute angle closure dramatically reduces the risk of developing acute attacks in these fellow eyes(12,13).

However, the benefits of iridotomy in asymptomatic patients with PACS is unclear. There is an on-going Cochrane review aiming to address this(14).

Given the raised pressure we could consider performing a peripheral iridotomy to break the pupil block mechanism. The anterior chamber area increases in patients who have APAC, who undergo LPI in both the APAC and fellow eyes(15). An alternative approach is to create space in the AC by removing the natural lens and replacing it with an artificial IOL which is much thinner. This is an alternative method of overcoming pupil block.

The literature informing the most effective treatment for PAC is limited. However, a recently undertaken randomised controlled trial, the EAGLE study(16), (Effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma), randomised patients with angle closure to either a laser Peripheral Iridotomy (LPI) or clear lens extraction and showed that lens extraction resulted in less need for drops and was more cost-effective than LPI as a first-line treatment for patients with PAC or PACG. Mean health status score was also higher in the clear lens extraction group. However, the degree of synechial angle-closure or visual field deficit at 3 years follow-up was not statistically significantly different between the two groups.

Current accepted practice would be to offer either YAG peripheral iridotomy or lens extraction as first-line treatment for those with PAC. When considering what options to adopt; discussion of the various risks and benefits of both LPI and cataract surgery should be discussed with patients to inform treatment choices.

References

1. Glaucoma: diagnosis and management | Guidance and guidelines | NICE [Internet]. [cited 2018 Jan 12]. Available from: https://www.nice.org.uk/guidance/ng81/chapter/Recommendations

2. Quigley HA, Broman AT. The number of people with glaucoma worldwide in 2010 and 2020. Br J Ophthalmol. 2006 Mar 1;90(3):262.

3. Day A, Baio G, Gazzard G, Bunce C, Azuara-Blanco A, Munoz B, et al. The prevalence of primary angle closure glaucoma in European derived populations: A systematic review. Vol. 96. 2012. 1162 p.

4. Foster PJ, Baasanhu J, Alsbirk PH, Munkhbayar D, Uranchimeg D, Johnson GJ. Glaucoma in Mongolia. A population-based survey in Hövsgöl province, northern Mongolia. Arch Ophthalmol Chic Ill 1960. 1996 Oct;114(10):1235–41.

5. Foster PJ, Oen FT, Machin D, Ng TP, Devereux JG, Johnson GJ, et al. The prevalence of glaucoma in Chinese residents of Singapore: a cross-sectional population survey of the Tanjong Pagar district. Arch Ophthalmol Chic Ill 1960. 2000 Aug;118(8):1105–11.

6. BMJ Publishing Group Ltd. BMA House TS. European Glaucoma Society Terminology and Guidelines for Glaucoma, 4th Edition - Chapter 2: Classification and terminologySupported by the EGS Foundation: Part 1: Foreword; Introduction; Glossary; Chapter 2 Classification and Terminology. Br J Ophthalmol. 2017 May 1;101(5):73–127.

7. Foster PJ, Buhrmann R, Quigley HA, Johnson GJ. The definition and classification of glaucoma in prevalence surveys. Br J Ophthalmol. 2002 Feb;86(2):238–42.

8. Foster PJ, Aung T, Nolan WP, Machin D, Baasanhu J, Khaw PT, et al. Defining “occludable” angles in population surveys: drainage angle width, peripheral anterior synechiae, and glaucomatous optic neuropathy in east Asian people. Br J Ophthalmol. 2004 Apr 1;88(4):486–90.

9. The Classification of Primary Angle-Closure Glaucoma | SpringerLink [Internet]. [cited 2018 May 14]. Available from: https://link.springer.com/chapter/10.1007%2F978-3-540-69475-5_5

10. Thomas R, George R, Parikh R, Muliyil J, Jacob A. Five year risk of progression of primary angle closure suspects to primary angle closure: a population based study. Br J Ophthalmol. 2003 Apr 1;87(4):450–4.

11. Thomas R, Parikh R, Muliyil J, Kumar RS. Five-year risk of progression of primary angle closure to primary angle closure glaucoma: a population-based study. Acta Ophthalmol Scand. 2003 Oct 1;81(5):480–5.

12. Snow JT. Value of prophylactic peripheral iridectomy on the second eye in angle-closure glaucoma. Trans Ophthalmol Soc U K. 1977 Apr;97(1):189–91.

13. Lowe RF. ACUTE ANGLE-CLOSURE GLAUCOMA*. Br J Ophthalmol. 1962 Nov;46(11):641–50.

14. Le JT, Rouse B, Gazzard G. Iridotomy to slow progression of angle-closure glaucoma. Cochrane Database Syst Rev [Internet]. 2016 [cited 2018 May 14];2016(6). Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4991823/

15. Moghimi S, Bijani F, Chen R, Yasseri M, He M, Lin SC, et al. Anterior Segment Dimensions Following Laser Iridotomy in Acute Primary Angle Closure and Fellow Eyes. Am J Ophthalmol. 2018 Feb;186:59–68.

16. Azuara-Blanco A, Burr J, Ramsay C, Cooper D, Foster PJ, Friedman DS, et al. Effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma (EAGLE): a randomised controlled trial. The Lancet. 2016 Oct 1;388(10052):1389–97.


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